Transmitter



Patented Aug. 12, 1930 UNITED STATES PATENT OFFICE ARTHUR BESSEY SMITH, F EVANSTON, ILLINOIS, ASSIGNOB TO RESERVE HOLDING- COMPANY, OF KANSAS CITY, MISSOURI, A CORPORATION OF DELAWARE TRANSMITTER I Application filed October 8, 1928. Serial No. 311,020.

This invention relates in general to improvements intelephone transmitters, but more particularly to an improved type microphone element structure for transmitters of the carbon granule type, and the principal object is to provide a microphone structure that is more eflicient and reliable in operation than those known heretofore.

I A further object is to design a micro hone structure which will more eifectively distribute the granular carbon in the microphone cell and still maintain a low resistance path for the current to flow through the carbon, when the transmitter is tilted in any desired position when in use.

In accordance with these and other objects not specifically mentioned but which will be apparent, the microphone structure designed according to the invention is arranged so that the current flow through the carbon granules extends over two separate paths at the same time, one path being in a direction substantially transverse to the lines of pressure as applied to the carbon granules by the vibrating diaphragm, andthe other path extending parallel with the lines of 1 pressure as is the usual practice in transmitters.

There are three electrodes in the microphone cell, one being arranged in the center of the rear of the cell to which one of the incoming wires lead, and the other two electrodes connected in parallel to the other wire. One of the last electrodes is spaced directly opposite the single rear electrode, while the other one comprises the inside circular wall of the microphone cell enclosure.

Between the two oppositely spaced center electrodes and the electrode comprising the wall of the microphone cell, there is arranged an insulated cup-shaped flanged member extending into the cell from the vibrating diaphragm. When the transmitter is in use, this insulated flanged member vibrates and breaks up the carbon granules, so they cannot become packed and thereby hinder the eiiicient operation of the microphone. This flanged member also directs the current flow through the carbon granules so that the transmitter may be tilted at any angle and still operate efliciently.

The foregoing and other useful objects are attained through means which will now be fully described, reference being had to the accompanying single sheet of drawings, showing in a sectional elevation a transmitter comprising a preferred embodiment of v the invention.

Except for the microphone structure, the transmitter may be of any well-known design, that shown in the drawing being one example. It comprises a mouth piece 1; face plate 2, having an opening into which the mouthpiece 1 is screwed; a heavy flanged ring 3 screwed into a threaded flange on the rear of the face plate 2; a bridge piece 7 formed integrally with the ring 3; the transmitter shell 4 which completely closes and protects the transmitter; and a microphone cell supported in the center of the bridge piece 7. A flat ring 6 of insulating material placed on the back side ofthe face plate 2 forms a rest for the main diaphragm 5 which receives the speech vibrations.

The microphone element consists essentially of the brass cup 9, the inside surface of which is gold plated or otherwise treated to form one of the electrodes; the circular rear electrode 16; the front electrode 16; the insulating flanged member 18; the granular mass of carbon around and between the electrodes; and the coupling arrangement between the auxiliary diaphragm 17 and the main diaphragm 5. The opening of thecupshaped electrode 9 is closed by the auxiliary diaphragm 17 which is made of very thin conducting metal. It is held against the brass cup 9 by the brass clamping ring 8 which has a threaded flange that engages the exterior threaded part of the cup 9. An insulating ring or washer 14 is also calmped between the diaphragm 17 and the clamping ring- 8 so as to absorb any irregularities that may be in the diaphragm 17. v 95 The circular front electrode 15 has an extended threaded shank which extends through the center of the diaphragm 17 It is clamped to the diaphragm by the clamping disk 13 and a nut 10 threaded on the 100 extended shank of the electrode. The insulating flange member 18 is clamped to the diaphragm between the diaphragm and the front electrode. The mam speech diaphragm 5 is clamped to the shank ofthe electrode 15 between two nuts 11 and 12, so that the diaphragm and the auxiliary diaphragm 17 will vibrate in unison when the transmitter is in use.

The round rear electrode 16 lies in the bottom of the cup 9 and is insulated therefrom by the insulating washer 20. The extended shank of this electrode 16 extends through a hole in the cup 9 and is insulated from the cup and the bridge piece 7 by the insulating bushing 26.

Spaced on the insulating bushing 26 between the bridge piece 7 and the cup 9 is the terminal plate 21 lying against the cup 9, and the insulating strip 22'which lies next to the bridge piece 7. This terminal plate 21 serves to carry current to the cup-shaped electrode 9 and the front electrode 15, while an additional terminal plate 24, insulated from the bridge piece 7 by the insulating washer 23, carries current tothe shank of the electrode 16. A nut 25 screwed onto the shank of the electrode 16 secures the whole microphone assembly onto the bridge piece 7 as a unit.

The operation of this transmitter will now be described, when it is in use and connected to a'telephone line, the wires leading from the bindm screw on the terminal plate 21 and from t e terminal plate 23. With current flowing over the line the following path for the current flow takes place: from the wire attached to the terminal plate 21, through this plate to the brass cup 9 and the inside electrode surface of the cup, through the carbon granules in the cell and around the insulating flanged member 18 which exerts a varying compression at the point 19 to the rear electrode 16, and thence to the terminal plate 24 and the wire attached thereto. In addition to this path, another path extends in parallel with the first path, but from the cup electrode 9 it divides and flows to the metal auxiliary diaphragm 17, clamping ring 13 to the front electrode 15, thence across the space 28 through the carbon granules to the rear electrode 16. The front electrode 15 exerts a varying compression in the space 28.

All current flow takes place over these two paths, and as the main diaphragm 5 is vibrated by speech variations and the auxiliary diaphragm 17 the front electrode 15 and the insulating flanged member 18 vibrate in unison therewith, the carbon granules in the cell in the vicinity of the spaces 19 and 28 are agitated a greater amount at these places than anywhere else in the cell. As it is across these spaces 19 and 28 that the current flow takes place, it will be seen that in this microphone cell there will be no place where the current can take a low resistance path and thus lessen the efficiency of the transmitter. Furthermore, the ackin of the carbon ranules is practical y eliminated in the cell no to the insulating flanged member 18 havin a large surface extendin into the granu es to thoroughly agitate t em when the current is flowin Due to the fact tllatthere are two paths for the current to fiow through the micro phone cell and that the insulating flanged member 18 extends part way into the cell throu h the carbon granules, it is impossible for t is transmitter to become open circuited. In other words, no matter what position the transmitter is held in when in use the current flow through the microphone cell will not be interrupted due to the carbon granules not being in contact with the electrodes.

When the transmitter is held in normal sition, as shown in the drawing, the caron granules adjust themselves as indicated, with the micro hone cell not'filled completely so as to allow or the contraction. and expansion, commonly called breathing of the granular mass when the diaphragm 17 vibrates. The current path through the microhone cell is as has been ex lained; from the inside electrode surface of t e cup 9, through the granular mass and the space 19 of the greatest agitation to the rear electrode 16 or at right an les to the movement of the diaphragm; an from the front electrode 15 through the granules in the space 28 where the greatest agitation takes place in that region to the rear electrode 16 or in the same direction as the movement of the diaphragm. Turning the transmitter about a horizontal axis through its center will not afiect its efficient operation in any way.

, Should the transmitter be held at an acute angle or face downward, it may be possible to interrupt the current flow extending through the granular mass at the space 19; but the other current path extending through the granular mass at the space 28 between the front electrode 15 and the rear electrode 16 would be in any event still be effective and thesuccessful operation of the transmitter would not be im aired in any way. 3

If the transmitter be held in a position so that it is face up or at some similar angle, its successful operation would not be hindered because the current path would be continuous from the inside surface of the on electrode 9 through the granular mass an the space 19 to the rear electrode 16. At the same time it may be possible to interrupt the other path extending through the granular mass at the space 28 from the front electrode 15 to the rear electrode 16.

It will thus be seen that in case the current flow through one of the paths inthe microphone should be interrupted the other path will always be effective to maintain the transmitter in efficient operation. This feature is very desirable for the type of transmitter used in the so-called cradle type of telephone in which the transmitter and receiver are combined into a single unit and is usually held at various different angles when in use.

From the foregoing description it will be apparent that a very eificient type of microphone unit has been designed which combines the two modes of granular carbon microphonic action, the usual contact resistance with electrodes, and the mass compressionaction.

While only the preferred embodiment of the invention has been described and illustrated, it is, however, to be understood that it is capable of a large number of variations, and it is therefore desired to be limited not to the precise construction shown, but only by the scope of the appended claims.

What is claimed is:

1. In a telephone transmitter, a microphone cell comprising a cupshaped electrode forming said cell and a moving diaphragm for closing the opening thereof, a second electrode attached to the bottom of and insulated from said cup electrode, a third electrode attached to said diaphragm opposite said second electrode, and granular resistance material in said cell in cont-act with all of said electrodes and forming a double current path extending from two of said electrodes to the other electrode.

2. In a telephone transmitter, a micro phone cell comprising a cup-shaped electrode, a moving diaphragm for closing the end of said cup electrode, a second electrode on the bottom of and insulated from said cup electrode, a third electrode on said diaphragm opposite said second electrode, and granular resistance material in said cell in contact with said electrodes and forming two current paths, one path extending from said cup electrode to said second electrode, and the other path extending from said third electrode to said second electrode.

3. In a telephone transmitter, a microphone cell comprising a cup-shaped electrode and a moving diaphragm for closing the opening thereof, a rear electrode attached to the, bottom of and insulated from said cup electrode, a front electrode on said diaphragm opposite said rear electrode, and-a double current path in said cell composed of granular resistance material, one path extending from said front electrode to said rear electrode parallel to the movement of said moving diaphragm, and the other path extending from said cup electrode'to said rear electrode, transverse to the movement of said diaphragm.

4. In a telephone transmitter, a cupshaped electrode forming a microphone cell,

a moving diaphragm for closing the opening of said cell, a rear electrode attached to the bottom of and insulated from said cup electrode, a front electrode on said diaphragm spaced opposite said rear electrode, and granular resistance material in said cell in contact with said electrodes, and forming two current conducting paths extending from saidcup electrode and said front electrode to said rear electrode, one path being parallel to the movement of said diaphragm and the other path transverse thereto.

5. In a telephone transmitter, a cups'haped'electrode forming a microphone cell, a moving diaphragm closing the opening of said cup, a rear electrode supported in the bottom of and insulated from said cup electrode, a front electrode supported on said moving diaphragm, granular resistance material. in said cell in contact with said electrodes, and a flanged insulating member on said moving diaphragm extending into said granular material between said cup electrode and said rear electrode for agitating said gpanular material to prevent packing there 0 6. In a telephone transmitter, a cupshaped electrode forming a microphone cell, a moving diaphragm closing the opening thereof, a rear electrode supported in the bottom of and insulated from said cup electrode, a front electrode supported on said moving diaphragm and spaced opposite said rear electrode, granular resistance material disposed in said microphone cell and in contact with said electrodes, a flanged insulating member on said diaphragm surrounding said front electrode and extending into said granular material, and a current path formed by said granular material extending in two directions and separated by said insulating member, one direction being transverse to the movement of said diaphragm and said insulating member and the other being parallel thereto.

7 In a telephone transmitter, a microphone cell comprising a cup-shaped electrode and a moving diaphragm closing the opening thereof, a rear electrode supported in the bottom of and insulated from said cup electrode, a front electrode supported on said moving diaphragm opposite said rear electrode, granular resistance material in said microphone cell in contact with said electrodes, and a flanged insulating member supported on said moving diaphragm and extending into said microphone cell between said cup and said rear electrode, and a double current path formed by said granular material separated by said insulating member and extending in two directions from said rear electrode.

8. In a telephone transmitter, a microphone cell comprising a cup-shaped electrode, a moving diaphragm closing the opening thereof,a rear electrode supported in t e bottom of and insulated from said cup electrode, a front electrode mounted on said moving diaphragm opposite said rear electrode, granular resistance material in said microphone cell in contact with said electrodes, and a flanged insulating member supported on said moving diaphragm and extending into said granular material between said cup and said rear electrode, said material occupying a restricted space around the end of said insulating flanged member and another space between said front and rear electrodes for forming a current path extending in two directions from said rear electrode to said other electrodes.

9. In a telephone transmitter, a micro phone cell comprising a cup-shaped electrode with a moving diaphragm closing the opening thereof, a rear electrode supported in the bottom of and insulated from said cup electrode, a front electrode supported on said moving diaphragm opposite said rear electrode, granular resistance material in said cell in contact with said electrodes, a flanged insulating member supported on said moving diaphragm and extending into said granular material between said cup and rear electrodes, said flange operative to agitate said granular material to prevent packing thereof, said granular material occupying a restricted space around the edge of said flanged member and another space between said front and rear electrodes, and a current path formed by said material extending in two directions from said rear electrode through both of said restricted spaces to said cup and said front electrodes.

10. In a telephone transmitter, a microphone cell and a movin diaphragm for closing the opening thereo an electrode formed on the inner surface of said cell, a second electrode attached to the bottom of and insulated from said cell and from first electrode, a third electrode attached on said diaphragm opposite said second electrode, and granular resistance material in said cell in contact with all the said electrodes.

11. In a telephone transmitter, a micro+ phone cell and a moving diaphragm for closing the opening of said cell, an electrode attached to the bottom of and insulated from said cell, a second electrode attached to said through said cell comprising granular resistance material, one path extending from said front electrode to said rear electrode parallel to the movement of said diaphragm, and the other path extending from said side electrode to said rear electrode, transverse to the movement of said diaphragm.

13. In a telephone transmitter, a microphone cell and a moving diaphragm for closing the opening of said cell, an annular electrode on the inside surface of said cell, a rear electrode supported in the bottom of and insulated from said cell, a front electrode supported on said moving diaphragm, a flanged insulating member supported on said moving diaphragm surrounding said front electrode and extending into said cell between said rear electrode and said annular electrode, and granular resistance material in said cell for forming two current paths extending from said rear electrode to said front electrode and said annular electrode.

In witness whereof, I hereunto subscribe my name this sixth day of October, A. D.

ARTHUR BESSEY SMITH. 

